1. Field of the Invention
The present invention relates generally to video recording and playback. More particularly, the invention relates to the optical writing and reading of data with respect to a storage medium such as a flexible optical tape.
2. State of the Art
Presently, flexible tape for optical storage of data is known, as described in U.S. Pat. Nos. 4,719,615 and 4,912,696, both identified on their cover page as being assigned to Optical Data, Inc. To optically record data on a medium such as a flexible optical tape, a scanning beam of laser light can be directed onto the tape. The laser beam melts the tape or burns holes in the tape to produce data spots representing bits of data. The data spots thus have a reflectivity, transmissivity or other optical characteristic which can be distinguished from the background of the optical tape.
Use of a laser to establish data spots representing bits of digital data or analog data on the flexible tape must be selected with practical limitations in mind. For example, in moving a laser back and forth across a moving tape, there is a limit to how rapidly the optical characteristics of a spot on the tape can be altered to form a data spot. Such a limit can be significant when, for example, the information being recorded corresponds to the video information of a television signal having a relatively high bandwidth. Further, such a limitation can be significant when attempting to optimize space efficiency in recording plural data spots on the optical tape.
For example, a relatively low intensity laser can be used to record the data spots on the tape. However, this requires that the tape be moved relatively slowly thus limiting the ability of the system to record high bandwidth signals in real time.
Alternately, an extremely high power laser can be used to record data spots. However, such lasers are extremely expensive and thus limit the commercial benefit to designing an optical recording and playback system which can be used as, for example, an optical video recorder (i.e., VCR). Further, when using a powerful laser with an optically sensitive tape, relative movement between the laser and the tape must be established which will permit the recording of relatively high bandwidth television video signals.
For example, to facilitate subsequent reading of data which is recorded using the known modified frequency modulation (MFM) technique, a one to two micron data spot included in a set of variable size data spots should be recorded such that it is spaced from a succeeding data spot by one to two microns of tape space. This prevents overlapping of the spots while optimizing space efficiency. To optimize the use of a high intensity laser to record these high bandwidth signals efficiently on the optical tape, the laser must be able to scan quickly back and forth across the tape. However, implementations of such high velocity deflection typically incur additional expense which, as noted above, hinders commercial feasibility of an optical VCR.
Plural low intensity lasers can be combined so that their beams overlap on the recording medium. However, such systems cannot be practically extended beyond the use of two overlapping laser beams. Although dual beam systems are cost effective in increasing laser light intensity, they are very awkward. This is especially true when the combined laser beam must be rapidly scanned to exploit the increased intensity.
It would therefore be desirable to provide an optical system capable of writing and reading high bandwidth spots onto flexible optical tape. However, to provide a cost effective system, it would be desirable to use one or more relatively low intensity, low cost lasers which do not require rapid scanning. Assuming that these competing criteria (i.e., high bandwidth signal recorded by a slow scan, low intensity laser) can be satisfied, it would be desirable to exploit the recording capability in a commercial environment, such as an optical VCR for television signal recording.